This is particularly important when bulk adding (by director, etc.)
as otherwise the user might end up having to click OK to many
many error dialogs.
Fixes: lp:1764057
* https://bugs.launchpad.net/kicad/+bug/1764057
Factor out the FP_LIB_TABLE specific content from FP_TBL_MODEL into a new
LIB_TABLE_GRID class that can be used for any library table grid mix in.
Create new FP_LIB_TABLE_GRID object for the footprint library edit dialog.
Add method GetEnvVariables() to return any environment variables found in
a LIB_TABLE object.
jean-pierre charras
Jeff Young
Oliver Walters
Wayne Stambaugh